The present invention is an improved process for the heat-fractionation of a mixture comprising an organosilane and a borane or borane forming compound. The improvement comprises the presence of a tertiary organoamine or tertiary phosphorous compound at a concentration sufficient to reduce modifications of the organosilane during the heat-fractionation process.
Methods are known in the art for the production of organosilanes having one or more aryl or cycloalkyl substitutions on the silicon atom. Such processes typically involve the reaction of an aromatic compound or cycloalkane with a silicon hydride in the presence of a Lewis acid as catalyst. The preferred Lewis acid catalyst in such processes is a trihalide boron compound or an organoboron compound. The present inventors believe that in such processes the trihalide boron compound or organoboron compound is reduced to a borane by the silicon hydride to form the active catalytic specie. The present inventors also believe that during conduct of subsequent heat-fractionation processes to isolate the desired organosilanes from the reaction product mixture, borane can act as a redistribution catalyst causing reduced yield of the desired product. Unexpectedly, the present inventors have found that when mixtures comprising an organosilane and a borane or borane forming compound are heat-fractionated in the presence of a tertiary organoamine or tertiary organophosphorus compound redistribution of the reaction product mixture to less commercially desirable compounds can be reduced.
Barry, U.S. Pat. No. 2,572,302, describes a process where a benzenoid hydrocarbon is reacted with an organodichloromonohydrosilane in the presence of boron halide to form aromatic organohalosilanes.
Brewer, U.S. Pat. No. 2,594,860, describes a process where a mixture comprising dichlorosilane and tetrachlorosilane is reacted with benzene in the presence of a boron halide to form phenyltrichlorosilane.
Barry, U.S. Pat. No. 2,626,266, describes a process where a benzenoid hydrocarbon is reacted with trichlorosilane in the presence of a boron halide to form a reaction product where aromatic halosilanes constitute a major portion.
Wagner et al., U.S. Pat. No. 2,775,606, describe a process where a mixture comprising trichlorosilane and dichlorosilane is reacted with benzene to produce a reaction product having as the major component phenyldichlorosilane.
Wright, J. Organometallic Chemistry 145:307-314 (1978) describes the reaction of benzene with trichlorosilane in the presence of boron trichloride to form phenyltrichlorosilane. Wright also discusses possible mechanisms for the catalytic activity of the boron trichloride in the process.
Gohndrone, U.S. Pat. No. 5,118,829, describes a process for substituting cycloalkyl substituents for a silicon-bonded hydrogen on a silane. The process employs a preformed organoboron compound as a catalyst.
The described art does not recognize that boranes, particularly in situ formed boranes, can act as a catalyst for detrimental processes in subsequent heat-fractionation steps to isolate preferred organosilane products. Furthermore, the describe art does not recognize that tertiary organoamines and tertiary organophosphorus compounds can reduce modification of organosilanes in mixtures comprising an organosilane and a borane or borane forming compound during a heat-fractionation process.